The present invention relates to a method and apparatus for detecting a banked curve driving condition to maintain operation of an electronic stability control of a vehicle driven thereon.
An electronic stability control (ESC) detects vehicle conditions and provides stability control to prevent vehicle rollovers, reduce skidding and maintain vehicle control during turning. In instances where a vehicle is driven on a banked curve, however, acceleration values and other information provided to the ESC does not conform to expected values. Thus, the ESC typically is not fully operative under such conditions.
FIG. 1 shows a vehicle 20 provided on a banked curve 22 that has a banked curve at an angle α relative to horizontal. The banked curve 22 also has a banked curve radius R (sharpness of the turn of a road of the banked curve) that is not capable of illustration in FIG. 1 and defines the degree of the curve. “V” in FIG. 1 represents vehicle velocity and “g” represents gravity (acceleration of about 9.8 meters/second). Without the vehicle 22 being located on the banked curve, lateral velocity of the vehicle is V2/R. When the vehicle 20 is on the banked curve at angle α, the lateral acceleration is (V2 cos(α)/R)−g sin(α)/R, which always has a value less than V2/R. Thus, for a vehicle 20 on a banked curve 22, lateral acceleration is always less than expected on a flat horizontal surface due to the banked surface. Further, vertical acceleration for a vehicle 20 traveling on a banked curve 22 is greater than expected for most vehicle speeds that are driven on banked roads, relative to a vehicle not provided with a banked curve. Vertical acceleration of the vehicle is defined as vertical to the road surface and vehicle. Thus, vertical acceleration is not in the direction of gravity as on an unbanked road. As shown in FIG. 1, the vertical acceleration is g cos (α)/R+V2 sin(α)/R. Due to the additional component from the lateral acceleration, the vertical acceleration for the vehicle 20 in a banked curve 22 is greater than the value g. Therefore, when both the angle α and the bank curve radius R is known, along with the easily measured vehicle velocity, direct calculations result in values for lateral acceleration and vertical acceleration. Moreover, when driving in a banked curve, the vertical acceleration is almost always greater than the typical vertical acceleration g and the lateral acceleration is less than the typical lateral acceleration expected for the particular driving speed, yaw rate, steering angle and other measureable operating values.
In a vehicle operating system, values for the banked curve angle α of a road and for the banked curve radius R are not easily determined. Therefore, the invention is directed to a cost effective approach for determining that a vehicle is being driven on a banked curve, without requiring sensing or calculating values for banked curve angle α and/or for banked curve radius R.